What is it? BMW’s long-awaited third-generation electric car isn't just electric. The upcoming four-seat i3 will be the first electric car from a mainstream automaker with an optional range-extending engine, as well as the first production vehicle that makes extensive use of carbon fiber in the body. At first this sounds a lot like the Chevrolet Volt, but the Volt's engine isn't optional.

The i3 is about 151-inches long, 79-inches wide, and five-feet tall, with a 101-inch wheelbase, making it a little shorter and wider than a Nissan Juke.

It weighs 2,630 pounds, significantly less than some other compacts, even with its 22-kWh lithium-ion battery. BMW says the i3 should be able to drive farther on a charge than other pure-electric cars: 80-100 miles according to the company's estimates. The optional 34 hp, 650cc twin-cylinder range extender engine mounted underneath the cargo floor comes from BMW’s motorcycle lineup. A 2.4-galllon gas tank in the nose of the car can add an additional 60 miles between refills. Whether operating as a pure electric or with the gasoline engine acting as a generator, ultimately, a 170-hp electric motor drives the rear wheels.

What’s new or notable? Almost everything. Building an electric car out of carbon fiber has long been the holy grail for efficiency, because moving less weight allows the battery to be smaller, lighter, and cheaper to get the same range. And the challenge for plug-in electric cars has been to dramatically downsize the gas tank and engine to offset the extra size, weight, and cost of the battery compared with gas-powered cars. BMW has fully employed both strategies here.

In addition, the i3 will be sold along with a suite of services BMW is calling 360 Electric, which includes a home charger, free access to a network of public chargers, and car sharing through the DriveNow network for long road-trip needs.

CR’s take: We were impressed with the performance of BMW’s Active-E coupe, which uses a similar powertrain. But the aggressive motor braking that aids battery charging took some getting used to.